One of the building blocks of today's optical networks is the Wavelength Selective Switch (WSS). A WSS comprises a common port and several tributary ports for input and output of optical signals to be switched, e.g. Wavelength Division Multiplexing (WDM) channels. In fiber-optic communications WDM is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. Through an electronic control interface, a WSS may be (re)configured to switch or route any of the incoming WDM channels on the common port to one of the tributary ports, irrespective of how other incoming wavelengths are routed. That is, on a single WSS, wavelengths may be routed between the common and tributary ports.
To create a more flexible wavelength routed switch two or more WSS devices may be interconnected in a particular way. Currently, the interconnecting WSS devices is the technology of choice to bring more flexibility to the WDM switching systems for transport networks, e.g. for local interconnection of different access segments in broadband communications networks. A problem with this is the complexity of the architecture and the increased cost due to the use of more than one WSS. That is, the required number of WSS elements and the required number of ports per WSS rapidly increases with the number of directions of an optical interconnect comprising such WSSs.
Optical Cross Connects (OXC) and Re-Configurable Optical Add Drop Multiplexers (ROADM) are examples of basic building blocks of transparent optical networks, which utilize switching in the optical domain. An OXC serves as an interconnection node between a number of fibres and/or directions, capable of routing wavelengths between the different directions in a reconfigurable manner. A degree of the OXC refers to the number of directions that are interconnected at the node. The ROADM may provide similar cross-connect functionality as the OXC and in addition also add/drop of wavelengths to/from local ports.
One of the problems with today's OXCs and ROADMs is the high cost associated with the number of required WSSs and WSS ports for introducing a desired flexibility or re-configurability.
The proliferation of broadband access to the Internet coupled with the introduction of new bandwidth-hungry applications, like video streaming and online gaming, over the last couple of years, have collectively led to an ever-increasing amount of traffic being exchanged inside communications networks, such as the internet. This trend has turned the design and operation of appropriate, cost-efficient transport networks into a major challenge for network operators. One of the main technologies used to realize transport networks is the optical communications and networking, which—thanks to the WDM concept—may provide larger transport capacities at a lower cost compared to the electronics counterparts.
Nonetheless, a problem is that the optical communications and networking technology is somewhat weak in providing flexibility, which is a significant requirement of advanced transport solutions in for example wireless communications networks.